Structure

ABSTRACT

A method for fabricating a space frame structure, such as a dome, for covering an open space, with the space frame structure being assembled from beam members, which intersect at rigid mode joints. The beam members and other structural components used in the skeleton of the space frame are made from pre-cast concrete, which has not been subjected to pre-tensioning and the rigid node joints are formed in situ, for example, by casting concrete joints incorporating the ends of the beam members. The loads imposed by the weight of the beam members on the beams and the node joints effectively simulate pre-stressing of the components which act within the assembled structure as pre-stressed concrete.

The present invention relates to a structure, notably to a system ofconcrete beams for forming a dome-like structure.

BACKGROUND TO THE INVENTION:

This invention relates to skeletal frame systems which supportfibreglass or other flexible, semi-rigid or rigid roofing sheets, panelsor glazing to provide a weatherproof or other cover or roof over largeopen spaces. Typical examples of where such systems find use are sportsfields, stadia, velodromes, athletic tracks, assembly buildings,stockpile covers, leisure facilities, aircraft hangers, open planfactories, train or bus stations, vehicle garages or stores and thelike. For convenience, such potential uses for the systems will bedenoted herein in general by the term covered open spaces.

Such systems usually require that the roof structure should not besupported by internal pillars, since these would interfere with the freeuse of the internal space of the covered open space and, in some cases,would obstruct the view of spectators.

Large span structures, that is structures which have a clear span lengthof 50 meters or more, have traditionally been constructed using steel asthe structural material. Large span steel structures which aresubstantially planar require out of plane strutting to provide stabilityand to enable the structure to be self-supporting and to carry itsdesign load. This can result in a mass of secondary steelwork, which isnot only expensive, but is also visually unattractive. The presentinvention relates to the construction of three-dimensional structures,for example domes and the like, where the roof structure extends inthree dimensions over an open space. Such structures comprising discretemembers rigidly joined together are commonly known as space frames.Typically, the radially outward periphery of the frame subtends an angleof 10° or more (preferably, 10° to 30°) to the horizontal. However, suchframes may progressively flatten towards their apex so that the anglesubtended to the horizontal decreases, often to zero or near zero at theapex of the frame.

A space frame is a structure in which a plurality of individualcomponents are linked together via rigid joints to form the overallstructure. For convenience, the term node joint will be used herein todenote one of the points within the overall structure at which aplurality of the components, for example tubes, rods, bars or beams, areinterconnected or jointed together to form the structural framework ofthe space frame. The node joints are substantially rigid so that theycan transmit moments from one component of the structure to another. Aspace frame is typically a three dimensional structure.

A typical form of such a space frame comprises steel bars having screwthreaded ends, which are interconnected at the node joints by means ofmachined steel blocks with threaded holes into which the threaded endsof the bars engage. It will be appreciated that by their very nature thebars and blocks have to be made to close tolerances. Furthermore, inorder to minimise sagging of the metal bars and to keep their transversethickness within acceptable limits, the bars have to be comparativelyshort. This requires the use of a large number of joints to achieve alarge span structure. This makes such structures complex and expensive.

Another form of a space frame uses tubular steel members welded togetherat the node joints. The individual tubular members are usually cut fromlengths of tube and require the formation of complex shapes at the endsthereof to provide a good fit of the components upon one another at thenode joints where typically three, four or more tubular members engageone another. Whilst such members and the node joints could bemanufactured off site, it is usually necessary to finalise the exactshape and dimensions of the ends of the tubular members on site asconstruction of the space frame proceeds. In addition, the individualcomponents have to be assembled into the space frame on site, whichrequires the use of high towers to support the assembled components inposition and subsequent welding of the components at each node joint toform the overall structure. This is complex, costly and often hazardousfor the construction operatives.

A fundamental characteristic of a space frame is that all joints at thenodes have to be rigid in the structural sense, i.e. capable oftransmitting moments and shears in the X, Y and Z axes and to resisttwisting about any of these axes. Traditional designs of such structuresusing conventional fabrication methods can only achieve thisthree-dimensional rigidity with cumbersome and expensive joints. Weldingof tubular components, or threading of solid bars into solid jointingblocks does achieve this rigidity, but only at a high cost and usingcomplex fabrication techniques.

In steel space frames the dominant cost element will be the joints,whether welded tubular joints or machined and screw threaded blocks.However, reducing the number of joints by increasing the length of theindividual bar or beam members is often not possible since thecompressive stresses which may be permitted in steel drop off rapidly asthe members increase in length, due to buckling considerations. Thislimits the maximum length of the members which can be used in any givencase and the number of joints which can be omitted is thus limited.

Concrete is known and used as a structural material. However, concretewhich has not been pre-stressed has, even with reinforcement, hithertobeen considered suitable only for short span beams and to be too heavyand weak for large span structures. Established engineering practiceshave limited the use of concrete in long span structures to the use ofpre-stressed concrete. However, where the tensioning wires or rods in apre-stressed concrete beam or other member are tensioned after themember has been cast, problems are encountered due to in situ corrosionof the wires or rods leading to structural failure of the components.Such materials are not advocated for use in structures which are to beexposed to the elements and where a long operating life is required.Where the tensioning is introduced into the rods or wires before theyare incorporated into the concrete during casting of the concretecomponent, the problem of corrosion is not evidenced. However, the costof fabrication of such components becomes excessive for large andone-off components and it is impractical to fabricate large pre-stressedcomponents on site without expert operators and complex equipment.Furthermore, difficulties and excessive costs may arise in transportinglarge pre-stressed concrete components from the site of manufacture tothe site of use. Accordingly, pre-stressed concrete is not considered aviable material for use in fabricating a large span space frame.

The use of steel as the material from which large span space framestructures are built is currently accepted as the only practicalalternative. This is despite the limitations on the length of theindividual components, the complexity of the jointing techniquesrequired to achieve three dimensional rigidity and need to maintain thestructure against rust, for example by painting the exposed steel work.This often requires that the covered open space enclosed by the spaceframe structure be taken out of use during the painting operation.

There thus exists a need for a structurally and commercially viablealternative to the use of steel to construct large span space frames.

The major loading on individual components in a large span space framestructure, especially one made from concrete, is a dead load due to theweight of the components. We have found that, in a three dimensionalstructure such as a dome, this load is converted to high axial forceswithin the beam members of the space frame structure. We have found thatthese forces can be used to advantage in a large span structure to actupon concrete beams which have not been pre-stressed and to simulate theeffect of pre-stressing the concrete beams. This discovery enables aconventional cast concrete or reinforced concrete beam to be used in aspace frame construction. Such a material offers the designer advantagesof cost savings and flexibility in design. For the constructor, the useof pre-cast concrete permits components to be manufactured to morerelaxed tolerances than steel components and for the tolerances to beaccommodated in node joints which are formed in situ. The use ofconcrete components which have not been pre-stressed enables theconstructor to use simple conventional concrete casting techniques tomake the beams and other components of the space frame structure on siteand the ability to form the rigid node joints in situ. This allows theconstructor flexibility in accommodating variations in the length of thebeams and in the geometry of the structure during fabrication of thespace frame structure.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a three dimensional spaceframe structure comprising a plurality of beam members inter-connectedat rigid node joints and having a clear span of 50 meters or more,characterised in that:

a. at least some of the individual beam members of the structure areformed from pre-cast concrete which has not been pre-stressed; and

b. the node joints- between the concrete beam members are substantiallyfully rigid in all three axes.

Broadly, the method of the present invention comprises the steps oflifting a first plurality of pre-cast concrete beam members intoradially extending positions and temporarily supporting them in thosepositions, lifting a second plurality of pre-cast concrete beam membersinto circumferentially extending positions spanning said radiallyextending beams and temporarily supporting them in those positions.

Preferably, the structure comprises a series of individual pre-castconcrete beam members extending generally radially from a central hub orapex and interconnecting with one or more, preferably generallyconcentric, rings formed from pre-cast concrete beams extendinggenerally circumferentially, the radial and circumferential beams beingconnected to one another at rigid node joints whereby the jointingbetween the beams provides a structure which is substantially rigid inthree dimensions. Preferably, the node joints are formed by castingconcrete joints between the beams in situ in the assembled structure.

In a particularly preferred aspect, the invention provides a space framestructure comprising a plurality of pre-cast concrete first axiallyelongated beam members jointed together in a radial arrangement whenviewed in plan view, at least some of the first beam members beingjointed to one or more rings of circumferentially extending pre-castconcrete second axially elongated beam members by joint members, thefirst members being angled to the horizontal at at least the radiallyoutward periphery of the structure, and the joint members beingsubstantially rigid joints between the members.

In such a structure, the second beam members act as partial supports forthe first beam members and thus reduce the bending moments anddeflections along the length of the first beam members. The rigid jointmembers enable the full bending strength of all the intersectingmembers, that is major axis bending, minor axis bending and torsion, tobe mobilised at the joints, thereby providing enhanced stability againstbuckling due to changes in geometry of the structure under load.

The invention also provides a method for fabricating a large span spaceframe structure, which method comprises supporting a plurality ofpre-cast concrete beam members in the desired location and orientationto form the structural elements of the space frame and securing the beammembers to one another by rigid joints.

Preferably, the beam members converge at node points and rigid nodejoints are formed at the node points by incorporating the ends of thebeam members at the node point in a rigid joint which is cast in situ.

In a particularly preferred embodiment of the method of the inventionthe components of the space frame structure are assembled in the desiredlocation and orientation upon temporary support members and the rigidnode joints are cast in situ and allowed to cure to form a rigidself-supporting space frame structure and the temporary support membersare progressively removed.

The invention can be applied to the construction of structures of a widerange of shapes, for example domes which have a square, rectangular,circular, oval or elliptical plan shape and which have a curved orpolygonal vertical cross section in which the angle the beam memberssubtend to the horizontal can be from 10 to 30° and may vary from suchan angle at the radially outward periphery of the structure to a valueof zero or near zero at the apex of the structure. The structure mayconverge at its apex to a single hub or point or to an annular ridgemember; or may converge to a generally horizontal or bowed linear ridge,for example in the case of a structure having an oval plan shape.

The structures may also comprise secondary structural members whichextend between the radial and/or circumferential main beam members, suchas Z purlins, struts and cross beams, which may be used to impart addedrigidity to the structure. The term beam will therefore be used hereinto denote in general all such axially extended components, whether theyprovide the main radial or circumferential members of the structure orare secondary members.

As indicated above, the invention is especially applicable to large spanstructures, that is structures which have a clear unsupported span of atleast 50 meters, typically 75 to 175 meters or more. The number ofradial beams in such a structure may vary with its size and, in general,the larger the span, the greater the number of radial beams which arerequired to form a rigid structure without excessive circumferentialspans between adjacent radial beams. If desired, a single radial beammay bifurcate at a node joint to provide two or more radial beamsextending radially outward from the node joint to reduce the spanbetween adjacent radial beams radially outwardly from that node joint.In plan view, the included angle between the circumferential beams at agiven node joint will depend upon the number of radial beams radiatingfrom the central hub or apex of the structure. We have found that thisincluded angle should in general be less than 160°. It is particularlypreferred that there should be less than 16, typically 4 to 14, notably6 to 12, radial beams radiating from the central hub or apex of thestructure and from 1 to 5 rings of circumferential beams intersectingthose radial beams; and that the plan angle included between thecircumferential beams at the node joints is from 90 to 150°, notably 110to 150°. Where the structures contain nearly straight portions, as withelliptical or oval plan shape structures, the included angles at thenode joints in such portions may be nearer, but less than, 180°.However, the majority of the node joints in such structures will be lessthan 150° and may be as low as 90° in the case of square or rectangularplan shape structures.

The structures are not truly circular in plan shape where the beammembers are straight beams. The terms concentric and circumferential asused herein are therefore to be construed as including not onlystructures having a circular plan shape, but structures which have apolygonal plan shape, including square or rectangular plan shapes.

The structure may rest directly upon foundations at ground level or maybe supported above ground level by piers, buttresses, walls or otherstructures which support the radially outward portions of the radialbeams above ground level. Such supports can be of conventional designand construction and can be vertical or inclined radially inwardly oroutwardly.

For convenience, the invention will be described in terms of a domestructure having a generally circular plan shape and converging to acentral solid or annular hub, with the curvature of the surface of thedome decreasing from an angle of from 15 to 20° to the horizontal at itsouter periphery to about zero degrees at the hub, and with an includedangle between the circumferential beams at a node joint of about 120°.

The concrete beam members may be of any suitable dimensions, for exampleexceeding 40 meters in length, and may be either cast on site or castelsewhere and delivered to the site of the structure for assembly onsite. The term pre-cast is therefore used herein to denote that theconcrete member is formed before it is incorporated into the structureas opposed to being cast in situ. As stated above, the concrete members,notably the beam members, are not pre-stressed, that is the members donot contain rods, bars, cables or other tensioning members which havebeen tensioned before or after the casting of the concrete members toapply significant axial compressive stresses to the components beforethey are incorporated into the space frame structure.

The individual members of the skeleton of the space frame may be formedeither as solid concrete and/or reinforced beams or other members.However, the beams may be cast as hollow members, for example hollow boxor tubular beams, using conventional techniques. The use of hollow beamsis preferred for longer spans, since this provides a beam having agreater stiffness for a given weight than a solid beam. The use ofhollow beams also enables the designer of the structure to locate wiringand service ducts, for example drainage or ventilation ducts or accesswalkways, within the beams and thus improve the visual and safetyaspects of the structure. If desired, one or more reinforcementmaterials, for example steel rods or mesh, or carbon, glass or polymerfibres, or woven, non-woven or reticulate materials can be incorporatedinto the concrete member. Whilst such reinforcement may be subjected totensioning if desired to ensure that it is uniformly deployed within theconcrete as it is cast, such tensioning is not sufficient to introducesignificant axial compressive forces into the concrete componentcontaining it so that the component is substantially non-pre-stressedwhen it is incorporated into the space frame structure.

The individual beam members may be of constant cross section along theirlength, or may be tapered both in width or depth or both. Alternatively,they may have a curved surface in cross section. The individual membersmay be straight or curved along their length. As described below,individual short beam members can be jointed together to form longerbeam members using the rigid jointing techniques described below to forma longer unitary beam member to aid transport, storage and handling ofthe shorter beam members.

The terminal portions of the beam members are linked to one another toform the desired rigid joint at each nodal joint. The terminal portionsof the beams can thus engage with a metal jointing spider of suitableconfiguration to form a temporary mechanical joint which is then madepermanent and rigid by casting concrete around the joint in situ. Thejointing spider can take a wide range of forms, for example metal fishplates or other connectors extending radially from a suitable hub towhich the ends of the beams are bolted. Alternatively, the ends of thebeams at a node joint can be provided with axially extending plates,bars or other members, for example the projecting terminal portions ofreinforcing rods within the concrete of the beam, which inter-engagewith or oppose to those on the ends of other beam members at the nodejoint to form a lapped structure which can be imbedded in concrete toform a permanent rigid joint. If desired, some of the inter-engagingrods can be screw threaded and engage suitable sockets carried by acentral spider or hub or by other beam members to form a temporarymechanical joint to support the beam ends at the node joint until thepermanent joint is formed. If desired, hoops, U bars, mesh or otherreinforcement can be wound around or incorporated into this structureprior to formation of the permanent joint.

In a further alternative, the spider may take the form of a series ofradial sockets carried by a central hub, into which the ends of the beammembers and/or the axially extending rods engage. If desired, thesockets can be a tight fit upon the ends of the beams and can beprovided with screw or other means for drawing the ends of the beamsinto the sockets to the desired extent to accommodate manufacturingvariations in the length of the beam members. Alternatively, the socketscan be provided with clamping means for tightening the socket upon theend of the beam, once the end of the beam has been engaged into thesocket to the desired extent.

For convenience, the term temporary mechanical joint will be used hereinto denote all such forms of temporary joint which are then incorporatedinto the permanent rigid node joint.

The spider or other mechanical joint can enclose the node joint so thatit provides part or all of the shuttering for containing the fluid orsemi-fluid concrete as the permanent joint is formed. Alternatively,conventional wooden or plastic shuttering boards, troughs or channelscan be provided around the node joint to retain the concrete and thenremoved once the joint has set.

At the apex of the construction, the ends of the beams can engage oneanother as described above to form a node joint at the apex.Alternatively, the apex is provided with a discrete hub member to whichthe ends of the beam members are jointed to form the apex of the spaceframe structure. The ends of the beams engaging the solid or annular hubat the apex of the structure can be jointed to the hub in a similarmanner to that described above for forming the node joints between thebeam members. The hub may be formed as a solid or hollow disc or thelike, or as a pre-cast ring member. Alternatively, the hub may be formedin situ from a series of short radial and annular beam members. The hubmay have a central aperture, for example to provide ventilation to theenclosed open space within the dome; or the aperture can be closed byone or more transverse walls or diaphragms as they are known in theconstruction industry which transmit radial forces diametrically acrossthe disc or ring of the hub. The radially outward face of the hub mayincorporate a radial flange or a series of radial sockets or other meansupon or into which the ends of the radial beams members engage toprovide temporary support for the radial beams until the rigid jointbetween the beams and the hub can be formed. If desired, bolts or othermeans can be provided to secure the ends of the beam member to the huband to provide a measure of radial adjustment to the position of thebeams to accommodate variations in the length of the beams and the wallthickness of the hub member.

The hub, the ends of the radial and circumferential beams intersectingat a node joint and any associated temporary mechanical joint aresupported in the desired configuration by a temporary structure, forexample a scaffolding or other tower of any suitable design andconstruction. This enables the node joints and the remainder of thespace frame structure to be assembled and supported in the assembledconfiguration. The shuttering or other means for retaining the concretein place around the joints during setting of the concrete can also besupported in position by these temporary support structures. Thetemporary support structures can then be progressively removed once allthe permanent joints have cured sufficiently for the space framestructure to become rigid and self-supporting.

The material used to form the in-situ cast joint at the node and otherjoints may have a cementitious base, be concrete, an epoxy resin orother chemical bonding compound. For convenience, the invention will bedescribed hereinafter in terms of the use of concrete for the in-situcast joint. The joint can incorporate fibre, rod or other reinforcement,for example the materials used to form the temporary mechanical jointbetween the intersecting members at the node. The joint can be formed byany suitable technique, for example by pouring, injecting, spraying,ramming, packing, trowelling the fluid or semi-fluid concrete mixtureinto the spaces in the joint structure to encase the temporarymechanical joint and the ends of the beams members and finishing off theexposed surfaces of the joint with a trowel or other smoothing device.

It will be appreciated that by forming the rigid joint in situ as thestructure is assembled, variation in the dimensions of the individualmembers, notably their length, can be accommodated to a greater extentthan with a fabricated steel space frame. However, this relaxedtolerance in dimensions means that secondary members to be attached atspecific points to the main beams, such as Z purlins, which are usuallyprefabricated to exact dimensions, may require modification on site, forexample by drilling holes in the secondary beams, to fit to mountingsprovided at desired locations on the main beams.

However, drilling the fixing holes on site is time consuming. Whilst thefixing holes in the ends of the secondary beams and/or the mountingbrackets carried by the main beams could be elongated into slots so asto accommodate variations in the length of the main beam members, thismay not provide a sufficiently rigid connection between the main andsecondary beam members for many conditions. We have devised analternative means for accommodating variations in the length of the mainbeam members which uses a screw, cam or other mechanism engaging a fixedanchorage point on the main or secondary beam and which adjustably movesa mounting bracket into register with mounting bolts or holes in the endof the beam to be secured to that mounting. Typically, the main beamscarry transversely extending bolts, studs or the like cast into theconcrete of the main beam at the locations where the secondary beam isto be attached. The mounting bracket is preferably L shaped and isprovided with a slot in one arm of the L into which two of those boltsor studs engage to permit the bracket to move axially and/ortransversely upon the main beam. The bracket is provided with twoopposed eye bolts, whose eyes engage with the shanks of the bolts orstuds of the main beam protruding through the slot in the bracket. Thepositions of the two eyes with respect to the slot can be adjusted bynuts, screw, cam or other mechanisms. The position of the bracket uponthe main beam member can be adjusted by slackening off one eye bolt andtightening the other so that the bracket moves axially with respect tothe bolts extending through the slot. By tightening both eye boltsaxially outward with respect to the slot, the eyes will secure themounting bracket firmly upon the main beam at the desired position. Inthis way the position of the bracket can be adjusted to accommodatevariations in the dimensions of the main beam without the need to modifythe secondary beam. It will be appreciated that the adjustable mountingbracket can be carried by the secondary beam rather than by the mainbeam.

If desired, during the fabrication of the temporary joints at the nodejoints or the secondary beams, a rapid setting resin can be injectedinto the joint to form an initial joint which is sufficiently strong tohold the members in the desired positions whilst shuttering isconstructed around the joint and concrete poured into the shutteredspace to form the permanent rigid joint in situ. If desired, at leastpart of the work in forming the joint can be carried out from within thebeam member where this is a hollow beam.

Where the beam member is a hollow beam, the rods, etc extending axiallyfrom the end thereof will usually be around the periphery of the beam.It may be desirable to form an internal transverse wall or diaphragm ator adjacent the open end of the beam so as to provide a mechanical linkto the annular joint formed when concrete is poured into the intersticesbetween the inter-engaging rods or the like. This link transfers loadsfrom the beam ends through the joint to other beam members incorporatedinto the node joint. This wall can be provided with one or more accessopenings for services and men into the main body of the beam. Thediaphragm wall can be provided with radially extending rods or the liketo inter-engage with the rods etc extending from the ends of other beamsor the joint member to provide further reinforcement and inter-linkingof the beam members and the jointing material of the permanent joint.

For longer spans, the length and weight of a single beam required tospan a node to node distance may be excessive for ease of fabrication onsite or transportation from a remote manufacturing location. It iswithin the scope of the present invention to form such long members intwo or more sections which are jointed together as described above onthe ground on site or in situ during the erection of the space framestructure to provide a unitary longer beam member.

It will be appreciated that accurate alignment vertically, horizontallyand rotationally of the sections used to form such a longer member isimportant and we have devised a method by which a high level ofalignment accuracy can be achieved. In this method, each section of theoverall member is supported on two supports, located in the length ofthe beam near to the lifting points of the individual beam members. Eachsupport has a PTFE or other low friction surface and has previously beenlevelled up using shims, screw adjusters of other means. Each support isprovided with a screw or other mechanism for moving the member sidewaysrelative to the support, whereby the sections of the overall member aremanoeuvred into straight-line alignment with one another. The sectionsare linked to one another by a push/pull system, for example a screw,cam or other mechanism, which adjusts the gap between adjacent sectionsto achieve the desired axial dimension for the overall unitary beammember. The sections can then be permanently jointed together using thetechniques described above. This procedure achieves correct alignment ofthe individual sections within the overall unitary beam member.

The formation of a unitary beam member from individual shorter beammembers achieves a precise length foro the overall jointed member, sincethe unitary member can be assembled after the initial shrinkage of theindividual beam sections as they dry out and cure h as taken place. Thisovercomes the problem of estimating the shrinkage which may take placewhen the overall beam is cast as a single component.

Whilst the invention has been described above in terms of nodes at whicha plurality of individual beams are jointed to one another, it will beappreciated that radial beams need not be jointed at the node where theyextend in a straight line to either side of the node, but that a singlebeam passing through the node may be employed. We have found that thishas the effect of supporting a long beam at the no de intermediate itsends and thus of reducing the bending of the beams and of reducing theflexing and distortion of the beam under load to that which would beachieved using two shorter beams. However, the use of a long beamassists accurate alignment of the beam between adjacent concentricportions of the structure.

As stated above, the beam members can be hollow, and the use of hollowmembers provides a number of benefits. Thus, the interior of the beamcan be used to house service or ventilation ducts. The wall of the ducteffectively acts as a sound insulation to reduce the noise ofventilation equipment. This enables higher ventilation air velocities tobe used without the production of unacceptable noise levels within theenclosed open space of the dome or other structure. The walls of thebeam can be provided with air inlets and/or outlets to the hollow ductwithin, thus allowing the designer greater flexibility in optimisingventilation within the dome. The hollow beams can also be used toprovide the necessary ducting for smoke extraction systems. Since thewalls of the beams are made from concrete, the beams are substantiallyfireproof and superior to the metal ducts used in prior structures.

A hollow beam can also serve as a walkway or other pathway to permitaccess to the structure for repair or maintenance without the need toprovide external ladders or scaffolding or to take any part of theenclosed space out of use. Furthermore, access doors or hatches can beprovided in the top or side walls of the beam members to enable accessto the exterior of the structure without the need for external laddersor scaffolding, thus providing a more safe and secure access to the roofcladding for service and repair. As indicated above, it will usually benecessary to provide access openings and/or doorways or hatches in anytransverse diaphragm walls at the ends of the beam members.

It will be appreciated that the walls of the beam members are understress. It will therefore be preferred to ensure that any openingsformed in the outer or internal walls of the beams are provided withsome form of lining to carry the stress around the periphery of theopening; and that any corners in the openings are rounded to minimisethe generation of stress relief cracks within the wall of the beam.Thus, it will usually be desired to provide a substantial steel bandlining to any opening in a wall of a beam member and to anchor the bandinto the surrounding concrete of the beam wall, typically with shearstuds, the studs being welded to the band using conventional techniques.

Enclosing the services within the hollow beam members also has theadvantage that the services may be fitted at an earlier stage in theconstruction of the structure than where the services are to be fittedexternally. Normally, fitting of the services cannot commence until thedome structure is clad and weatherproof. Using the hollow beam members,service fit out can commence on completion of the structure or evenearlier. For example, the hollow beam members can be fitted out withsuitable service ducts and wiring or other facilities prior to beingincorporated into the structure. This has major cost and time savingimplications.

Where visual appearance is of minor importance, the permanent jointsbetween the beam and other members can remain exposed. However, in somecases it may be desired to mask the joints. This can be done bydecorating the joints in with the remainder of the structure. However,this may not be practical for many structures and it may be desirable toform the end of the beam with an axial extension sleeve which extends asa shroud over the exposed rods, etc which are to form part of the nodeor other joint. This shroud can form the external shuttering for theconcrete joint to be cast in situ and any axial gap between the shroudof one beam and those of adjacent beams or other components can bein-filled with a suitably coloured mastic, cement or other fillermaterial. Such masked joints are denoted as blind joints herein.

The invention has been described above in terms of forming the nodejoint in situ, optionally using temporary mechanical supports such asthe spider forming an integral part of the joint. However, it is withinthe scope of the present invention to pre-form part of the node jointand to incorporate that into the overall joint by casting concrete insitu at the junction between the pre-formed joint component and the endsof the beam members. The use of a pre-formed node joint is of especialbenefit where the beams are hollow and the node joint is complex. Thepre-formed joint can be made from any suitable material, for exampleconcrete, steel, glass or other fibre reinforced plastic or concrete,and can incorporate the transverse walls described above for the ends ofthe beam members.

Where a pre-formed node joint is used, it may be desirable to providelinkage members, for example screw threaded bolts or the like which canbe secured into sockets in the faces of the node joint or engage insuitable sockets in the opposing end faces of the beam members. In placeof screw threaded bars, plain profile bars may be used and those weldedto the opposing bars of the beam members. The pre-formed node joint maybe configured to provide the shuttering necessary for casting theconcrete in situ to form the rigid joint. Alternatively, the pre-formedjoint can provide the temporary mechanical linkage described above, andseparate shuttering used in the formation of the permanent rigid jointincorporating the pre-formed jointing member.

The space frame structure of the invention serves to support anysuitable roofing, glazing, netting or other cladding to provide anappropriate enclosure for the covered clear space within the structure.Thus, panels or sheets of clear or opaque material can be secured by anysuitable technique to the beams of the structure either directly orindirectly.

DESCRIPTION OF THE DRAWINGS:

The invention will now be described by way of illustration to thepreferred embodiments thereof as shown in the accompanying diagrammaticdrawings in which:

FIGS. 1a to 1 e show different geometrical shapes of space framestructures which may be achieved using the present invention;

FIG. 2 shows a partially assembled space frame of the invention;

FIG. 3 is a longitudinal sectional view of a hollow beam suitable foruse in the space frame structure of the invention;

FIG. 4 is a transverse cross sectional view of the beam of FIG. 3 andthe mould in which it is formed;

FIG. 5 is a longitudinal sectional view of a jointed hollow beam for usein the space frame structure of the invention;

FIGS. 6 to 8 illustrate equipment used for aligning short beams sectionsduring the fabrication of a jointed hollow beam of FIG. 5;

FIGS. 9 to 11 illustrate the formation of a rigid nodal joint in thespace frame structure of FIG. 2;

FIG. 12 is a horizontal sectional view of the nodal joint of FIG. 11;

FIGS. 13 and 14 are horizontal sectional views through a pre-formedjointing piece for use in the nodal joint of FIG. 12;

FIGS. 15 and 16 are sectional views through a modified nodal joint;

FIGS. 17 and 18 are transverse cross sectional views through a hollowbeam showing the presence of service ducts and access openings in thebeam;

FIG. 19 is a cross sectional view through a nodal joint showing thepresence of transverse walls at the end of the beams and openings inthose walls;

FIG. 20 illustrates details of the linings for openings in the wall of abeam;

FIGS. 21 to 23 illustrate an adjustable bracket for securing a secondarybeam to a main beam.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The space frame structures of the invention can take a number of formsas shown in FIGS. 1a to 1 e. The forms can be simple radial facetedcones as shown in FIG. 1a or curved roof domes as shown in FIG. 1b inwhich the feet of the radial beams are anchored directly into theground. Alternatively, the feet of the radial beams can be supportedabove ground by legs or feet as shown in FIG. 1c, which Figure alsoshows the bifurcation of the radial beams outwardly of a node point.Instead of the generally circular plan shapes shown in FIGS. 1a to 1 c,the structure can have an oval plan shape as shown in FIG. 1d or thesquared plan shape as shown in FIG. 1e.

As shown in FIG. 2, these structures are assembled from solid or hollowsection radial beams 1 and 2, which intersect and are jointed to one ormore rings of circumferential beams 3 at node points 4. The upper endsof the radial beams 1 are jointed to a hub 5, which can be a solid discas shown in FIG. 1a or can be an annular member with a central apertureas shown in FIG. 1e and FIG. 2.

The structure is assembled by raising the hub 5 and beam members 1, 2, 3into position using a crane or other lifting means and supporting themin the required position by means of scaffolding or other temporarysupport towers 6. The beam members converge at the node points 4 and apermanent rigid node joint (e.g., as designated by reference numeral 7in FIG. 11) is formed at the node points. Preferably, reinforcing orother rods, plates or other linkage members 8 extend axially from theends of the beams. These inter-engage or lap at the node points 4 andare incorporated into the ridge node joints 7 as described below to forma rigid structure. Once the joints 7 have been cured and the structurebecomes self supporting, the temporary support towers 6 areprogressively removed. As a result, the weight of the beam members 1, 2,3 develops

The beams are preferably cast on site at ground level using normalreinforced concrete casting techniques. A typical hollow beam 10 forpresent use is shown in FIGS. 3 and 4 and has axially extending metalbars or plates 8 at the ends thereof, for example the protruding ends ofthe reinforcing rods incorporated into the beams during casting. Suchhollow beams can be cast within a mould 11 using an inner former 12 andvibrators 13, shown in FIG. 4, to form a box section beam usingconventional casting techniques.

In some cases, the beam may be shorter than required. Two such beams 10can be jointed in end to end relationship to form a longer unitary beam14 as shown in FIG. 5. This is preferably achieved using the equipmentshown in FIGS. 6 to 8. For example, the two shorter sections of beam 10can be placed on PTFE support pads 15 which have been accuratelylevelled up using shims or screw adjusters to align the sections 10horizontally. The supports 15 are provided with screw operated sidewaysadjustment mechanisms 16 which can be adjusted to move each end of thesection 10 independently sideways until the longitudinal axes of thebeam sections 10 are coincident, the adjustments being monitored by alaser. The opposed ends of the sections 10 are provided with push/pullbolts 17 as shown in FIG. 7 so that the overall axial length of theunitary beam 14 can be adjusted to the desired value as shown in FIG. 8.The permanent joint between the opposing ends of the sections 10 canthen be achieved by pouring concrete between the opposed ends to encasethe rods 8 protruding from the opposing ends of the beams 10. Ifdesired, a jointing spider 18 of axially extending rods or plates can beinserted between the rods 8 to reinforce the joint.

The node joints 7 between the beams 1, 2 and 3 and between the beams 1and the hub 5 can be formed in a similar manner. Typically, as shown inFIGS. 9 to 12, the rods 8 extending axially from the ends of the beamssupported on towers 6 are intermeshed, optionally with an additionalspider or pre-cast jointing piece as shown in FIG. 12. Shuttering 20,where this is not already provided by the jointing piece, is formedaround the node point as shown in FIG. 10 and concrete poured to encasethe node point, the rods and the jointing piece as shown in FIG. 11. Ifdesired, further reinforcement, for example U bars and the like, can beincorporated into the joint.

Similarly, the inner ends of beams 2 engage in suitable slots orrecesses 16 in the hub 5 and a permanent rigid joint is formed there.

If desired, a purpose built open topped shuttering box can be made fromglass fibre reinforced polymer to the desired external shape of the nodejoint 7 and the ends of the beams 1, 2 and 3 laid into the open topchannels in the shuttering box and the concrete poured into the box toform the in situ joint.

A form of pre-formed jointing piece 40 is shown in greater detail inFIGS. 13 and 14. The jointing piece comprises a pre-cast concrete nodejoint core 40 having radiating arms 41 which are to engage the ends ofthe radial and circumferential beams 1, 2, 3 either directly or viaintermediate components to accommodate variations in the lengths of thebeams and the geometry of the joint. The joint core also comprises acentral nodal chamber 42 defined by the diaphragm walls 26 having therequisite duct or walkway 22 openings therein. The exposed ends of thearms 41 have protruding rods 43 or the like, for example the ends ofreinforcing bars, which are to be imbedded in the concrete forming thepermanent joint between the ends of the beams 10 and the jointing piece40. It will usually be preferred that the rods 43 have screw ends whichengage socket pieces in the ends of beams 10 to enable the jointingpiece 40 to be drawn up firmly upon the beams 10. If desired, thejointing piece 10 can incorporate external and internal shuttering 44,45 to retain the concrete in position around the jointed componentswhilst it sets and cures.

The resultant dome-like structure is a stable structure enclosing aninternal open space without the need for internal pillars or othersupports. Sheets of metal, plastic or other material can then be laidupon the framework and secured to the beams to provide a roofedenclosure.

Such a structure is simple and cost effective to build. However, thenode joints 7 and the joints around the doughnut may be visible andaesthetically unattractive due to the prominence of the joints and thefact that the colour of the concrete cast in situ for the joints may bemarkedly different from that of the beams.

A structure having less obtrusive joints and utilising hollow beams canbe fabricated using beams which have an axially extending shroud portion21 as shown in FIGS. 3 and 5 and in detail in FIGS. 15 and 16. Theshroud portion 21 extends axially as a thinner wall portion of the endof the wall of beam 10. Preferably, the shroud 21 does not extend forthe full circumference of the beam 10, but forms an open topped portionas shown in FIG. 16 into which the concrete can be poured, a former orshuttering (not shown) being inserted into the interior of the beam toact as internal shuttering to retain the concrete in position whilst itsets. If desired, any small space between the opposing end faces of theshrouds 21 on opposed beams 10 can be grouted or filled with mastic. Theopen top of the joint can subsequently be closed by casting a slab overit using normal concrete casting techniques.

The use of hollow beam members 10 enables service ducting and walkwaysto be incorporated within the beam structure, thus avoiding the need toprovide external access routes. For example, as shown in FIG. 17, theinterior of the beam may be provided with a ventilation duct 22. Asshown in FIG. 18, the wall of the beam can be provided with an accessopening 23 whereby an operator can gain access to the exterior of thebeam. In the case shown in FIG. 18, the access opening 23 is in the topwall of the beam 10 and provides access to the outer face of the sheetmetal or other cladding 24 used to cover the space frame structure ofthe dome via an external cabin 25 and door.

It will usually be desired to provide the opposed ends of the beams 10at the node joints 7 with transverse walls or diaphragms 26, as shown inFIG. 19. Such diaphragms serve to transmit forces from one component ofthe structure to another. Such diaphragms are preferably also providedwith openings for service ducts 23 or walkways 27 as shown. Suchdiaphragms may be incorporated into a pre-formed jointing piece 40 asshown in FIGS. 13 and 14 rather than at the ends of the beams 10.

Since the walls of the beams 10 are under stress, it will usually bedesired to provide any openings formed in the walls of the beams withsteel or other substantial linings 28 as shown in FIG. 20 and to roundany corners in such openings. The linings 28 are secured in place bymeans of studs 29 set into the concrete of the diaphragm 26 or the wallof the beam 10 and welded to the lining 28 as shown. Z purlins or othersecondary beams can be attached to the concrete framework formed by themain radial and circumferential beams by the adjustable mountingbrackets 50 shown in FIGS. 21 to 23. This is in the form of an L sectionplate. One arm of the L has an axial slot 53 which engages threaded studbolts 49 protruding transversely from the main concrete beam. Thebracket 50 carries two opposed eye bolts 51 extending axially inregister with the slot 53 and whose axial position with respect to theslot 53 can be adjusted by suitable nuts 52 engaging the threads of theeye bolts 51. The eyes of the eyebolts 51 are secured to the bolts 49 bynuts on the bolts 49. The other arm of the L of the bracket is toreceive the end of a purlin beam and to be secured thereto by bolts orother means. The position of the bracket 50 upon the main beam isadjusted by altering the position of the eyebolts 51 relative to theslot so that the bracket moves axially with respect to the stud bolts 49to bring other holes in the bracket into register with bolts in the endof the purlin beam without the need to adapt the purlin beam. Thebracket 50 is then locked in the desired position by drawing theeyebolts axially outward in opposite directions along slot 53 by meansof nuts 52.

What is claimed is:
 1. A method for constructing a large, open-spanframe structure, comprising the steps of: lifting a first plurality ofpre-cast concrete beam members into radially-extending positions andtemporarily supporting said pre-cast concrete beam members in saidradially-extending positions; lifting a second plurality of pre-castconcrete beam members into circumferentially-extending positionsspanning adjacent said pre-cast concrete beam members in saidradially-extending positions and temporarily supporting said pre-castconcrete beam members in said circumferentially-extending positions;and, forming rigid node joints between each said pre-cast concrete beammember in said circumferentially-extending position and said pre-castconcrete beam members in radially-extending positions which saidpre-cast concrete member in circumferentially-extending position spans,with an included angle between each said pre-cast concrete beam memberin said circumferentially-extending position at each said rigid nodejoint being from 90° to 160°.
 2. The method for constructing a large,open-span frame structure according to claim 1, wherein said rigid nodejoints are formed by casting concrete join in situ.
 3. The method forconstructing a large, open-span frame structure according to claim 2,wherein said rigid node joints incorporate mechanical joints aroundwhich said concrete joints are cast.
 4. The method for constructing alarge, open-span frame structure according to claim 1, wherein there arefrom 4 to 14 said pre-cast concrete beam members in saidradially-extending positions radiating from a central hub or apex saidlarge, open-span structure.
 5. The method for constructing a large,open-span frame structure according to claim 1, wherein at least some ofsaid pre-cast concrete beam members are hollow.
 6. The method forconstructing a large, open-span frame structure according to claim 5,wherein said pre-cast beam member which are hollow incorporatetransverse internal walls at, or adjacent to, the ends thereof.
 7. Amethod for constructing a large, open-span frame structure, comprisingthe steps of: lifting a first plurality of pre-cast concrete beammembers into radially-extending positions and temporarily supportingsaid pre-cast concrete beam members in said radially-extendingpositions; lifting a second plurality of pre-cast concrete beam membersinto circumferentially-extending positions spanning adjacent saidpre-cast concrete beam members in said radially-extending positions andtemporarily supporting said pre-cast concrete beam members in saidcircumferentially-extending positions; and, forming rigid node jointsbetween each said pre-cast concrete beam member in saidcircumferentially-extending position and said pre-cast concrete beammembers in radially-extending positions which said pre-cast concretebeam member in circumferentially-extending position spans, with saidpre-cast concrete beam members in said radially-extending positionssubtending an angle of from 10° to 30° to the horizontal at least at aradially-outer periphery of said large, open-span structure.
 8. Themethod for constructing a large, open-span frame structure according toclaim 7, wherein said rigid node joints are formed by casting concretejoin in situ.
 9. The method for constructing a large, open-span framestructure according to claim 8, wherein said rigid node jointsincorporate mechanical joints around which said concrete joints arecast.
 10. The method for constructing a large, open-span frame structureaccording to claim 7, wherein there are from 4 to 14 said pre-castconcrete beam members in said radially-extending positions radiatingfrom a central hub or apex said large, open-span structure.
 11. Themethod for constructing a large, open-span frame structure according toclaim 7, wherein at least some of said pre-cast concrete beam membersare hollow.
 12. The method for constructing a large, open-span framestructure according to claim 11, wherein said pre-cast beam member whichare hollow incorporate transverse internal walls at, or adjacent to, theends thereof.
 13. A method for constructing a large, open-span framestructure, comprising the steps of: lifting a first plurality ofpre-cast concrete beam members into radially-extending positions andtemporarily supporting said pre-cast concrete beam members in saidradially-extending positions; lifting a second plurality of pre-castconcrete beam members into circumferentially-extending positionsspanning adjacent said pre-cast concrete beam members in saidradially-extending positions and temporarily supporting said pre-castconcrete beam members in said circumferentially-extending positions;and, forming rigid node joints between each said pre-cast concrete beammember in said circumferentially-extending position and said pre-castconcrete beam members in radially-extending positions which saidpre-cast concrete beam member in circumferentially-extending positionspans, with at least some of said pre-cast concrete beam memberscomprising shorter beams which have been joined end-to-end by rigidjoints for forming a unitary longer beam member.
 14. The method forconstructing a large, open-span frame structure according to claim 13,wherein said rigid node joints are formed by casting concrete join insitu.
 15. The method for constructing a large, open-span frame structureaccording to claim 14, wherein said rigid node joints incorporatemechanical joints around which said concrete joints are cast.
 16. Themethod for constructing a large, open-span frame structure according toclaim 13, wherein there are from 4 to 14 said pre-cast concrete beammembers in said radially-extending positions radiating from a centralhub or apex said large, open-span structure.
 17. The method forconstructing a large, open-span frame structure according to claim 13,wherein at least some of said pre-cast concrete beam members are hollow.18. The method for constructing a large, open-span frame structureaccording to Claim wherein said pre-cast beam member which are hollowincorporate transverse internal walls at, or adjacent to, the endsthereof.
 19. A method for constructing a large, open-span framestructure, comprising the steps of: lifting a first plurality ofpre-cast concrete beam members into radially-extending positions andtemporarily supporting said pre-cast concrete beam members in saidradially-extending positions; lifting a second plurality of pre-castconcrete beam members into circumferentially-extending positionsspanning adjacent said pre-cast concrete beam members in saidradially-extending positions and temporarily supporting said pre-castconcrete beam members in said circumferentially-extending positions;forming rigid node joints between each said pre-cast concrete beammember in said circumferentially-extending position and said pre-castconcrete beam members in radially-extending positions which saidpre-cast concrete beam member in circumferentially-extending positionspans; and, providing secondary beam members between a main pre-castconcrete beam member in radially-extending position and a main pre-castconcrete beam member in circumferentially-extending position.
 20. Themethod for constructing a large, open-span frame structure according toclaim 19, wherein said secondary beam members are connected to said mainpre-cast concrete beam member in radially-extending position and saidmain pre-cast concrete beam member in circumferentially-extendingposition via adjustable mounting means.
 21. The method for constructinga large, open-span frame structure according to claim 19, wherein saidrigid node joints are formed by casting concrete join in situ.
 22. Themethod for constructing a large, open-span frame structure according toclaim 21, wherein said rigid node joints incorporate mechanical jointsaround which said concrete joints are cast.
 23. The method forconstructing a large, open-span frame structure according to claim 21,wherein there are from 4 to 14 said pre-cast concrete beam members insaid radially-extending positions radiating from a central hub or apexsaid large, open-span structure.
 24. The method for constructing alarge, open-span frame structure according to claim 21, wherein at leastsome of said pre-cast concrete beam members are hollow.
 25. The methodfor constructing a large, open-span frame structure according to claim24, wherein said pre-cast beam member which are hollow incorporatetransverse internal walls at, or adjacent to, the ends thereof.
 26. Amethod for constructing a large, open-span frame structure, comprisingthe steps of: lifting a first plurality of pre-cast concrete beammembers into radially-extending positions and temporarily supportingsaid pre-cast concrete beam members in said radially, extendingpositions; lifting a second plurality of pre-cast concrete beam membersinto circumferentially-extending positions spanning adjacent saidpre-cast concrete beam members in said radially-extending positions andtemporarily supporting said pre-cast concrete beam members in saidcircumferentially-extending positions; and, forming rigid node jointsbetween each said pre-cast concrete beam member in saidcircumferentially-extending position and said pre-cast concrete beammembers in radially-extending positions which said pre-cast concretemember in circumferentially-extending position spans, said rigid nodejoints incorporating pre-formed jointing pieces rigidly jointed to saidpre-cast concrete beam members in said circumferentially-extendingposition and said pre-cast concrete beam members in radially-extendingpositions.
 27. The method for constructing a large, open-span framestructure according to claim 26, wherein said rigid node joints areformed by casting concrete join in situ.
 28. The method for constructinga large, open-span frame structure according to claim 27, wherein saidrigid node joints incorporate mechanical joints around which sailconcrete joints are cast.
 29. The method for constructing a large,open-span frame structure according to claim 26, wherein there are from4 to 14 said pre-cast concrete beam-members in said radially-extendingpositions radiating from a central hub or apex said large, open-spanstructure.
 30. The method for constructing a large, open-span framestructure according to claim 26, wherein at least some of said pre-castconcrete beam members are hollow.
 31. The method for constructing alarge, open-span frame structure according to claim 30, wherein saidpre-cast beam member which are hollow incorporate transverse internalwalls at, or adjacent to, the ends thereof.
 32. A method forconstructing a large, open-span frame structure, comprising the stepsof: lifting a first plurality of pre-cast concrete beam members intoradially-extending positions and temporarily supporting said pre-castconcrete beam members in said radially-extending positions; lifting asecond plurality of pre-cast concrete beam members intocircumferentially-extending positions spanning adjacent said pre-castconcrete beam members in said radially-extending positions andtemporarily supporting said pre-cast concrete beam members in saidcircumferentially-extending positions; providing a hollow beam memberhaving a wall, said wall having an opening with said opening havingrounded corners and provided with a substantial lining thereto, which issecured to a material of said wall; and, forming rigid node jointsbetween each said pre-cast concrete beam member in saidcircumferentially-extending position and said pre-cast concrete beammembers in radially-extending positions which said pre-cast concretemember in circumferentially-extending position spans.
 33. The method forconstructing a large, open-span frame structure according to claim 32,wherein said rigid node joints are formed by casting concrete join insitu.
 34. The method for constructing a large, open-span frame structureaccording to claim 33, wherein said rigid node joints incorporatemechanical joints around which said concrete joints are cast.
 35. Themethod for constructing a large, open-span frame structure according toclaim 32, wherein there are from 4 to 14 said pre-cast concrete beammembers in said radially-extending positions radiating from a centralhub or apex said large, open-span structure.